You can't develop abdominal muscles in two or three months. What you should do now is to increase aerobic exercise, such as jogging for at least one hour every other day, and pay attention to your diet. If you want to eat meat, try to choose white meat, that is, fish and poultry, eat more vegetables, have dinner before six o'clock in the evening and don't eat after six o'clock. You can do push-ups and sit-ups in your spare time if you can't.